When Steve died wasn't that fridging for Tony, Bucky, Sharon, the Marvel universe at large etc?
Character death is always used to elicit emotion, often for the loved ones left behind.
The difference is that Steve was shown to have had such a huge presence in everyone's life that everyone was mourning him. His death was treated as a big deal because of who he was, not because of who specifically was mourning him.
Sharon dying, on the other hand, was shown to only matter in as far as Steve went. Despite being a SHIELD agent, Maria Hill didn't particularly care aside from how it was impacting Steve's psychological wellbeing.
I think the biggest problem with Sharon as a character and how she's been used over the last decade is that her two major defining moments are 1) being brainwashed and pumping multiple bullets into Steve's chest to "kill" him and 2) shooting Ian in the throat and "killing" a child. Her relationship with Steve is currently like a bad country song and she doesn't have much to do outside her relationship with Steve.
I'm not sure when either became defining character moments, and by who, exactly. The later, particularly, said a lot more about Remender than it did about Sharon.
Why is Sharon 'killing' Steve a 'defining moment' and her bringing Steve not?
Presumably the reason Stark crying at at Steve's memorial service is one from Tony and him dumping Steve's body in the arctic isn't.
As for Sharon getting a solo... Kind of an uphill battle, that, when people are selective in acknowledging what she does, or defending of her exclusion.